This invention relates to spatial light modulators that are based on micromechanically-actuated, diffractive mirror structures. A prior-art device in this category, the "Flat Diffraction Grating Light Valve" (U.S. Pat. No. 5,841,579), comprises two interdigitated groups of parallel ribbon reflectors, wherein one group is fixed and the other is electrostatically actuated to control the ribbons' surface heights. The device is dynamically controlled to function alternately as a plane mirror (with the ribbons' reflective surfaces all coplanar) or as a diffraction grating (with the movable ribbon surfaces recessed relative to the fixed ribbons). The device functions as a pixel element in a spatial light modulator that has applications to image displays and printing systems.
Advantages of the grating light valve are that it can operate under high illumination levels and at very high (e.g., megahertz-level) switching rates, and it can be used with broadband illumination. It is especially well adapted for display applications, although it could have potential limitations for applications such as high-resolution printing and maskless lithography that require smaller pixels and more precise control of the image illumination levels. The lithographically defined gaps between ribbons can limit efficiency and contrast, and performance could also be compromised by non-planarity of the elongated ribbon elements.